The present application claims priority to Japanese Application No. P2000-045150 filed Feb. 17, 2000, which application is incorporated herein by reference to the extent permitted by law.
1. Field of the Invention
The present invention relates to a novel monostable ferroelectric liquid crystal display apparatus using a liquid crystal material having a chiral smectic C phase.
2. Description of the Prior Art
Liquid crystal display elements have been widely used as light-weight thin type display elements. Among them, twisted nematic (TN) display elements of the TFT drive are especially widely used.
However, the aforementioned display element has various problems such as a tone reversal behavior in the middle tone, a narrow viewing angle, a slow response time such as several milliseconds or above, and the like. Especially the response time between the middle tones reaches as much as 100 milliseconds or above and the image display delay causes a tailing phenomenon.
In such a situation, a great expectation is posed on the ferroelectric liquid crystal as a liquid crystal material which improves the viewing angle and reduces the response time and its application for display is considered.
For example, Clark et al suggests a surface-stabilized ferroelectric liquid crystal display (SSFLCD) of the passive matrix drive method utilizing a bistable memory in which the helical pitch of the ferroelectric liquid crystal is untied in the narrow gap cell to realize bistability having two memory states (see Appl. Phys. Lett. 36, 899 (1980) and U.S. Pat. No. 4,367,924, Japanese Patent Publication 60-22287).
This SSFLCD has an advantage that it is possible to realize a white-black binary display element of a wide viewing angle.
However, for the image display speed increase, because of the passive matrix drive method, the response time for one pixel is as short as several microseconds but in the case of display having plenty of pixels, the speed is not always increased. Accordingly, the SSFLCD cannot be applied to the animation display in the multimedia era.
Furthermore, the number of pixels is gradually increased, starting in the so-called VGA, SVGA, XGA, SXGA, and UXGA. For the large-capacity display, a principle of high-speed display is expected.
To realize display of this high-speed response and wide viewing angle, the applicant of the present invention has suggested a monostable FLC mode in Japanese Patent Publication 4-212126 and U.S. Pat. No. 5,214,523.
This mode utilizes a liquid crystal element having a pair of substrates subjected to uniaxial orientation processing and arranged in such a manner that the orientation processing directions are almost in parallel to each other and a liquid crystal material having the chiral smectic C phase filled between the substrates. The component projected to the substrate in the axis direction of the cone drawn by the liquid crystal molecule of the liquid crystal material having the chiral smectic C phase and the component projected to the substrate in the molecule axis direction of the liquid crystal molecule itself are matched with the substrate orientation processing directions, respectively, which state is the initial state of the monostable configuration. A switching element is arranged for each of the pixels, i.e., the minimum unit for performing the active matrix drive. Voltage is applied to continuously change the liquid crystal director (molecule axis inclination) so as to perform analog modulation of the transmitting light intensity, thereby realizing an analog tone display of high speed and wide viewing angle as well as full-color display.
More specifically, a transparent electrode side of a glass plate on which a transparent electrode (ITO) is arranged is subjected to the silane coupling processing. After this, the spin coat method is used to apply a polyamide acid film, which is baked to form a polyimide film. This polyimide film is subjected to rubbing with a velvet cloth in one direction to obtain an orientated film. The orientated film has a thickness of about 200 Angstrom and is asymmetric with respect to the rubbing direction to obtain the liquid crystal orientation effect. Two of the glass plate each having the orientated film thus prepared are arranged in such a manner that the transparent electrodes oppose to each other and the rubbing directions are anti-parallel to each other, thereby assembling a cell with a 2-micrometer gap using an ultraviolet ray setting adhesive in which 2-micrometer micropal is dispersed. The liquid crystal material includes as the chiral component a compound (a) shown in Chemical Formula 2 below and as the non-chiral component, a tricyclic difluorine-based compound (b), phenyl pyrimidine-based compound (c), and phenyl benzoate-based compound (d), thereby realizing a monostable FLC mode. 
However, with the aforementioned liquid crystal composite material, it is impossible to obtain a sufficient black level sinking to obtain a sufficient contrast ratio. Moreover, the monostability of the aforementioned liquid crystal composite material when subjected to an electric field is insufficient.
Japanese Patent Publication 11-125182 discloses that the aforementioned liquid crystal composite material can increase the contrast ration when containing phenyl pyrimidine connected an alkyl chain having 17 carbons at the both ends. Moreover, Japanese Patent Publication 11-151755 discloses that the aforementioned liquid crystal composite material can increase its monostability when containing biphenyl pyrimidine connected to an alkyl chain having an even number of carbons at the both ends.
However, when the liquid crystal composition contains phenyl pyrimidine connected to an alkyl chain having 17 carbons at the both ends or biphenyl pyrimidine connected to an alkyl chain having an even number of carbons at the both ends, the melting point is increased and the liquid crystal material is crystalized at room temperature. For this, it is impossible to use a monostable ferroelectric liquid crystal apparatus prepared using this liquid crystal material at room temperature.
It is therefore an object of the present invention to provide a monostable ferroelectric liquid crystal display apparatus capable realizing a monostable mode with a sufficient stability even at room temperature and a sufficient analog tone and contrast ratio.
The inventors of the present invention, during development of a monostable ferroelectric liquid crystal display apparatus, found that a liquid crystal material containing dicyclic phenyl pyrimidine has a lowered melting point when the phenyl pyrimidine skeleton has one end connected to an alkoxyl chain and the other end connected to an alkyl chain wherein the sum of carbons in the alkoxyl chain and the alkyl chain is 15. This realizes a monostable mode specifically stable at the room temperature and improves the analog tone and the contrast ratio.
The monostable ferroelectric liquid crystal display apparatus according to the present invention includes: a pair of substrates, each subjected to uniaxial orientation processing and arranged so that their orientation processing directions are approximately parallel to each other; and a ferroelectric liquid crystal material having the chiral smectic C phase filled between the substrates, the liquid crystal material being such that the projection component of the cone drawn by a liquid crystal molecule of the ferroelectric liquid crystal material projected onto the substrate and the projection component of the liquid crystal molecule itself projected onto the substrate in the molecule axis direction are respectively identical to the orientation processing direction of the substrates, which state is the initial state of the monostable configuration, wherein the ferroelectric liquid crystal contains a compound having a phenyl pyrimidine skeleton having one end connected to an alkoxyl chain and the other end connected to an alkyl chain, wherein sum of carbons in the alkoxyl chain and the alkyl chain is 15.
By adding dicyclic phenyl pyrimidine having a phenyl pyrimidine skeleton having one end connected to an alkoxyl chain and the other end connected to an alkyl chain wherein the sum of carbons in the alkoxyl chain and the alkyl chain is 15, it is possible to realize a stable monostable FLC mode and significantly improve the analog tone, black level, and contrast ratio as well as lower the melting point although no detailed reason is known.